Medieval warming was global – new science contradicts IPCC

'It was consensual' claims looking shaky

Opinion More peer-reviewed science contradicting the "scientific consensus" was announced yesterday, as a new study shows that the well-documented warm period which took place in medieval times was not limited to Europe, or the northern hemisphere: it reached all the way to Antarctica.

The research involved the development of a new means of assessing past temperatures, to add to existing methods such as tree ring analysis and ice cores. In this study, scientists analysed samples of a crystal called ikaite, which forms in cold waters.

“Ikaite is an icy version of limestone,” explains earth-sciences prof Zunli Lu. “The crystals are only stable under cold conditions and actually melt at room temperature.”

Down in the Antarctic peninsula that isn't a problem, and Lu and his colleagues were able to take samples which had been present for hundreds of years and date their formation. The structure of Ikaite, it turns out, varies measurably depending on the temperature when it forms, allowing boffins to construct an accurate past temperature record.

A proper temperature record for Antarctica is particularly interesting, as it illuminates one of the main debates in global-warming/climate-change: namely, were the so-called Medieval Warm Period and Little Ice Age merely regional, or were they global events? The medieval warmup experienced by northern Europeans from say 900AD to 1250AD seems to have been at least as hot as anything seen in the industrial era. If it was worldwide in extent that would strongly suggest that global warming may just be something that happens from time to time, not something caused by minuscule concentrations of CO2 (the atmosphere is 0.04 per cent CO2 right now; this figure might climb to 0.07 per cent in the medium term).

The oft-mentioned "scientific consensus", based in large part on the work of climate scientists Michael Mann and Phil Jones and reflected in the statements of the Intergovernmental Panel on Climate Change (IPCC), says that isn't true. The IPCC consensus is that the medieval warming – and the "Little Ice Age" which followed it – only happened in Europe and maybe some other northern areas. They were local events only, and globally the world was cooler than it is now. The temperature increase seen in the latter half of the 20th century is a new thing caused by humanity's carbon emissions.

Lu and his colleagues' new work, however, indicates that in fact the medieval warm period and little ice age were both felt right down to Antarctica.

“We showed that the Northern European climate events influenced climate conditions in Antarctica,” says the prof, who was at Oxford when most of the work was done but now has a position at Syracuse uni in the States. He and his colleagues write:

This ikaite record qualitatively supports that both the Medieval Warm Period and Little Ice Age extended to the Antarctic Peninsula.

In other words, global warming has already occurred in historical, pre-industrial times, and then gone away again. Lu et al's work is published in the peer-reviewed journal Earth and Planetary Science Letters. ®